Long Exposures with D-SLR's?

[drh681]

the 20D has a feature for long exposures that entails the making of a "dark frame" immediately after your image. then you can use the dark frame to remove any sensor generated noise from the image.

as a general rule, digital cameras have worse "grain"(noise) at long exposure than does film. this can be overcome but requires something like the above feature.

IR work is possible with dslr cameras. In fact there is a guy that will remove the hot mirror from a camera for you making it a dedicated IR camera. I cant find the link so you will have to google "hanson fong"

also, I have had nice results with anHoya R72 filter on a Minolta S414 and I have seen very nice images in IR from Minolta's Dimage7 cameras.

[TimeZone]

drh681 & caerdruagh, thanks for the replys.

I found the article on the Nikon D2x interesting, but I am really looking to go with Canon since I already have Canon SLR film lenses and equipment.  Hopefully the Canon's can give similar performance to what the Nikon can with long exposures.  I have been impressed so far with what Canon has done with their digital equipment.

I did some research on the web and found some things that made it sound like the 20Da (special for astrophotography) could shoot long exposures of up to an hour.  I think the 20D can also, but I'm not sure.  I really don't want a special camera just for astrophotography, infrared, etc.  It would be nice if I had the extra money, but I will mainly shoot more normal type shots.  Really long exposures and other stuff is a bonus that I hope to be able to do. Moderate length exposure of 30 sec. up to a few minutes is more important.

One statement I found interesting on the Canon site was this:

* Manages with Shorter Exposure Time

The absence of low light reciprocity failure allows a shorter exposure time. To give an example, when taking photographs with the combination of an ISO 400 film and a f/2.8 lens, an exposure of 10 minutes is required, with some variations because of weather conditions.
But using an EOS DIGITAL camera with the same combination film with an ISO setting of 400 and a f/2.8 lens, the exposure takes only 2-3 minutes.

So perhaps the length of exposure I was thinking about would not even be needed with the digital cameras as opposed to using film, due to reciprocity.

Some interesting Canon 20Da images and info.
http://www.canon.co.jp/Imaging/eos20da/special/index03.html

One of these images is 45 minutes long and shows the star trails in it.

This Canon site has some information on using Canon digital cameras for astrophotography.
http://www.canon.co.jp/Imaging/astro/index-e.html

This was an interesting discussion on infrared with the 20D.
http://photography-on-the.net/forum/showthread.php?t=56595

I downloaded the 20D manual and read about bulb exposures where it mentioned a timer that went to 999 seconds.  This would be an exposure of over 16 minutes.  I wasn't sure if this was the limit for exposure length and/or with the noise reduction setting?  Hopefully thats not the limit on length.  Still, it would be more than enough for most long exposure needs.

Everything I have found made it sound like the 20D is excellent on long exposures.  I will probably get one around September, unless they have announced or released something better in the price range.

[TimeZone]

Remember that with digital exposures on a tripod-mounted camera that it is very easy to combine the exposures to give the effect of a much longer exposure.  The technique of adding together a series of short (say 30s to 1 min) exposures of the stars on a fixed tripod has also been done to create the effect of a longer exposure.

Graham, thanks for the reply.  I wonder if this would lead to a less noisy image (several 1 minute shots combined in Photoshop) compared to one longer exposure?  I  guess that it would perhaps, but would just have to experiment on this.  It seems that with this method your noise might be limited basically to your longest exposure depending on how they are blended in Photoshop.

I can see where this would work with astrophotography type of images where you have a dark background shooting mostly sky.   As the star formation moved you would capture light in new places creating a similar effect to a longer exposure done all at once or waiting longer between shots to create more of a multi-exposure look.

On many of my images though the main part of the images might be more of a landscape / cityscape.  Would stacking images work with non-moving images like these?  It doesn't seem like it would.  Each image would only capture the same light and not add up to more or would it?  For these type of images I think only a long exposure would work.

By the way, the Canon 20D doesn't seem to even offer a multi-exposure setting that I could find in the manual.  Maybe  I missed it.  This is probably better done in Photoshop by combing multiple images anyway though, as you mention, instead of taking chances and ruining your previous shot as in the days of film.

[lxdesign]

The Nikon D2h also does an excellent job at long exposures!

[TimeZone]

I was thinking about finally making the leap to digital with one of the Canon D-SLR's, probably the D20 unless a replacement comes out soon.

I am wondering if there are any limits to doing long bulb exposures with these cameras?

For instance I would like to experiment with long night exposures as done by Michael Kenna in some of his images. In one of his photos you can see the trails left by stars.  I believe some of the exposures can be several hours at a time, and perhaps require ND filters even at night.  Of course the work I am talking about was done with film.

I would also like to do some fairly long daytime exposures using ND filters as well.

Will this cause any problems with sensor noise, battery life, etc.?  Can it do it ok?  I think so, but wanted to ask. I know some cameras take an extra exposure to eliminate sensor noise.

I am guessing that the images should be less grainy, noisy, then long exposures with film?

Also, I don't guess there is anyway to really do infrared photography with the D-SLR's is there?

Thanks,

Lum

[caerdruagh]

A big jump in price, but the Nikon D2x can, according to Bjorn Rorslett, quite happily make exposures up to three hours:
http://www.naturfotograf.com/D2X_rev04.html

[gwarrellow]

Remember that with digital exposures on a tripod-mounted camera that it is very easy to combine the exposures to give the effect of a much longer exposure.  The technique of adding together a series of short (say 30s to 1 min) exposures of the stars on a fixed tripod has also been done to create the effect of a longer exposure.

A variant on this is a common procedure when taking guided astrophotos with CCD cameras or digital cameras.  Amongst other things it helps to reduce guiding errors and improve the signal to noise ratio of the image.

I would not recommend the modified Canon cameras unless you intend to use it almost exclusively for astrophotos.  If you are interested in the use of digital cameras for astro work you will find some very helpful advice on the Yahoo Digital Astro group
http://groups.yahoo.com/group/digital_astro/

good luck
Graham

[jani]

By the way, the Canon 20D doesn't seem to even offer a multi-exposure setting that I could find in the manual.  Maybe  I missed it.  This is probably better done in Photoshop by combing multiple images anyway though, as you mention, instead of taking chances and ruining your previous shot as in the days of film.

The camera itself doesn't do automatic multiple exposures at set intervals, no.

But with the remote timer/controller TC-80N3, you can do exactly that, and more. It's sensible to get a remote anyway, even though this one is a bit pricey.

Keep in mind that it's using a cable, so you might need to get an extension if you're going to stand further than a couple of meters from the camera.